1. Field of Invention
This invention relates generally to infrared heaters in which a refractory body is heated by means of a ribbon-type, gas-fired burner head to an elevated temperature causing it to emit infrared radiation, and more particularly to an infrared heater of this type adapted to supply heat energy to a cooking wok.
2. Status of Prior Art
The transfer of heat takes place by three processes: conduction, convection and radiation. In conduction, heat is transferred through a body by the short range interaction of molecules and/or electrons. Convention involves the transfer of heat by the combined mechanisms of fluid mixing and conduction. In radiation, electromagnetic energy is emitted toward a body and the energy incident thereto is absorbed by the body to raise its temperature. Radiant heating, therefore, differs from both convection and conduction heating, for the presence of matter is not required for the transmission of radiant energy.
According to the Stefan-Boltzmann law, the rate of heat transfer between a source of radiated heat whose temperature is T.sub.s and an absorbing body whose temperature is T.sub.b is equal to T.sub.s.sup.4 -T.sub.b.sup.4 ; that is, to the difference between the fourth powers of these temperature values. In convection heating, the rate of heat transfer is proportional only to the temperature difference between the body being heated and the surrounding atmosphere. Hence convection heating is inherently very slow, as compared to the nearly instantaneous effects of radiant heating.
My prior patents 4,507,083; 4,432,727 and 4,702,693 disclose infrared heaters in which a refractory body is heated by means of a ribbon-type burner to an elevated temperature causing it to emit infrared radiation. The ribbon-type burner is of the type disclosed, for example, in the Flynn U.S. Pat. No. 3,437,322, in which a gas-air fuel mixture is fed into a cylinder having a longitudinal slot therein occupied by a stack of corrugated ribbons to create an array of minute jet openings through which the gas-air mixture is expelled. Because of the myriad of jet openings, the projected flame is not composed of discrete jets but assumes a sheet-like form.
However, the intensity of the flame is not uniform throughout the length of the ribbon, for the pressure of the gas-air mixture in the cylinder is not equalized throughout its length. Hence, the resultant infrared radiation pattern is not of uniform intensity; and when food is subjected to this pattern, the heating thereof may be uneven.
In my above-identified copending patent application, there is disclosed a ribbon-type, gas-fired burner head usable as a heat source, which head may also be combined with a refractory body to form an infrared radiation heater. The burner head includes a pair of parallel plates having a circular, oblong or other configuration having a continuous contour free of discontinuities, and a stack of continuous corrugated ribbons having the same configuration sandwiched between the peripheral margins of the plates to define an internal fuel chamber.
Fed into this chamber through an inlet nipple attached to one of the plates is a mixture of pressurized combustion air and gaseous fuel in a stoichiometric ratio, the mixture being expelled from the chamber through an array of minute jet openings created by the stack of ribbons. By igniting the expelled mixture, there is projected from the head an omni-directional flame whose intensity is substantially uniform in all direction. The flame is directed at a refractory body to heat it to an elevated temperature, causing it to emit infrared radiation.
The present invention deals with an infrared heater of a type disclosed in my copending application which is adapted to supply heat energy to a wok. A wok is a bowl-shaped metal cooking utensil used mainly in the preparation of Chinese food, such as chopped up vegetables.
In wok cooking, a load of chopped up food ingredients is deposited in the central region of the bowl, cooking oil being added thereto. In the course of cooking, which takes place in a few minutes, the food is agitated by the cook so that it is spread into the annular region of the wok surrounding the central region.
The range or stove conventionally used for wok cooking is provided with ring-type gas burners whose flame is projected from the periphery of the ring. The wok is seated over the ring so that its center is aligned with the center of the ring. As a consequence, the heat supplied by the ring impinges on the wok in an outer region surrounding its central region. Hence the central region of the wok where most of the food load is deposited does not receive as much heat as the surrounding region, a condition which is less than ideal. Moreover, the stove counter on which the wok is placed has heat transferred thereto from the outer region of the wok, and this heat is radiated into the room in which the stove is installed, thereby raising it to an uncomfortable temperature.
It is for this reason that some ranges are provided with water-cooled coils to reduce the counter temperature. Stoves of this type therefore require both gas and water lines. A further drawback of such prior arrangements is that the BTU requirements for gas-fired burners are considerably higher than for infrared heaters supplying an equivalent amount of heat; hence they are more expensive to operate.